Radiotelephone system



Dec. 15 ,1925. 1,566,245

Q. A. BRACKETT RADIO TELEPHONE SYSTEM Filed Sept. 2, 1921 WITNESSES:INVENTOR 0mm Ema/fish.

W fi AT TORNEY Fin Patented Dec. 15,1925. 4

UNITED STATES .1, fi6,245 PATENT OFFICE.

Q'O'INCY A. BRACKETT, OF SPRINGFIELD, MASSACHUSETTS, ASSIGNOR TOWESTING-r HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OFPENNSYL- VAN IA.

RADIOTELEPHONE SYSTEM.

Application filed September 2, 1921. Serial No. 497,949.

To all whom it may concern: I

Be it known that I, QUINCY A. BRACKETT, a citizen of the United States,and a resident of Springfield, in the county of Hampden and State ofMassachusetts, have invented a new and useful Improvement inRadiotelephone Systems, of which the following is a specification.

My invention relates to wireless signaling systems and more especiallyto means for controlling the transmission of radiant energy.

In its broad aspect, the object of my invention is to provide animproved modulating system for use in connection with vacuumtubeoscillation generator systems, whereby the radio-frequency currentsgenerated thereby may be modulated in accordance with sound waves.

More especially, the object of my inven tion is to provide means forcontrolling the grid leak of an oscillator tube in accordance withmodulating currents, thereby admitting of the radiation of modulatedenergy.

In my invention, I provide an improved modulating system in which athree-electrode tube is provided with the customary grid condenser and agrid leak, the latter comprising a thermionic device, the impedance ofwhich is adapted to be varied in accordance with sound waves or othersignals to be transmitted.

Other objects of my invention, as well as details of construction,whereby my invention may be practiced, will be apparent in the followingdescription and claims, when read in connection with the accompanyingdrawings, wherein:

Fig. 1 is a diagrammatic view of circuits and apparatus embodying myinvention.

Fig. 2 is asimilar view, but showing alternative means for controllingthe value of the grid leak in accordance with sound waves, and

Fi 3 is a view similar to that of Fig. 2, but s owing analternative'type of modulator tube.

Referring to Fig. 1, an oscillator tube 1 comprises ananode 2, acontrofling grid 3 and a cathode 4, which may be energized by means of asource of energy 5 through a resistor 6, operatively associated with anantenna circuit and adapted to generate radio-frequency currents in amanner well known to the art. The antenna circuit comprises an antenna7, a tuning coil 8, a variable condenser 913116. a ground lead 10.

A plate-filament circuit of the oscillator tube 1, which comprises aportion 11 of the tuning coil 8 and the variable condenser 9, may beenergized from a source ofdirectcurrent energy 12 through reactors 13which are connected to opposite plates of the condenser 9.

A grid-filament circuit comprises a feedback coil 14, which isoperatively connected to coil 8, a condenser '15 for maintaining anegative charge upon the grid 3 and an adjustable grid-leak device 16which is connected in shunt relation to the condenser 15.

The adjustable grid-leak device 16 com rises a three-electrode tube, ofwell known orm, having .an anode 17, a control electrode 18 and acathode 19 contained therein. The cathode 19 is energized from a sourceof energy 21 through a resistor 22. The hot cathode 19 and the anode 17of the tube 16 are connected to opposite plates of the condenser '15which are connected, respectively, to the grid 3 and to the hot cathode1- of the oscillator tube 1. The variations in intensity of the soundWaves may be translated into corresponding modulating currents by meansof a circuit which includes a microphone transmitter 23, radiofrequencychoke coils 24 and a source of energy 25. The transmitter modulationsare impressed upon the grid 18 of the tube 16 as potential variationsthrough the transformer 26.

The arrangement shown in Fig. 2 diifers from that of Fig. 1 in the meansfor varying the impedance of the space-current path which is shuntedaround the grid condenser 15. In the modification just mentioned, I haveprovided a thermionic device 27 comprising an anode 28, which isconnected to the filament side of the condenser 15, and a hot cathode29'which is connected to the grid side of the condenser 15. hot cathode29 may be energized by means of a "source of direct-current energy 30,which is connected to the hot cathode 29 through the mocrophonetransmitter 23,.a battery 30, a resistor 31 and choke coils 32. Thechoke coils 32 have been so connected as to keep the radio-frequencycurrents from traversing the source of energy 30 and the microphonetransmitter 23, thereby elim- Thefilament 29 necessary to inating thecapacity effects in the elements just mentioned.

Although a oneway leak, such as disclosed in the previous figure, willoperate satisfactorily, the grid leak of the modification is of thetwo-way type. In Fig. 3, I have shown a simple form of thermionic tube33 which serves as a two-way grid leak. This thermionic tube 33, it willbe noted, differs from that shown in Fig. 2 in that the anode 28 hasbeen replaced by a hot cathode 34 which is similar to the hot cathode29. The hot cathode 34 may be energized from the source of energy 5through a resistor 35.

In operation, referring to Fig. 1, upon a supply of energy to theoscillator tube 1, and upon a proper adjustment of the constants of thecircuits associated therewith, sustained oscillating currents aregenerated in a manner Well known to the art.

The impedance of the tube 16 or, in other words, the rate of leakage ofthe negative charge from the grid 3 is then adjusted to such value that,upon speaking into the telephone transmitter 23, the radio-frequencycurrents, which are generated by the tube 1, are modulated in accordancewith the potential variations impressed upon the grid 18 of the tube 16.

Refer-ring to Fig. 2, the operation of the grid leak differs from thatof Fig. l in that the impedance of the space-current path is variedthrough the control of the filament temperature. In order to render thedevice properly responsive to such current variations as are produced inthe transmitter 23, it is apparent that a relatively fine filamentshould be employed.

Referring to Fig. 3, the operation of this system is similar to that ofFig. 2.

The thermionic tubes comprising the grid leaks shown in the drawings maybe either of the vacuum type or of the gas filled type, depending uponwhether a high resistance grid leak or a low resistance grid leak isdesired. The temperature variations in the reduce effective modulationmay be lowered by employing a tube filled with some gas such as hydrogenhaving the special characteristics found valuable in flash lighttelegraphy.

In its broadest aspect, my modulating system is applicable as a repeateror an amplifier in any electrical signaling system employing eitherunidirectional or oscillatory carrier-ciu'rents. My invention may bealso adapted to wireless telegraph communication by replacing thetelephone transmitter 23 by a telegraph key, as will be obvious to thoseskilled in the art.

While I have described three forms of my invention, many minor changes,alterations and modifications may be made without de parting from thespirit thereof. I desire. therefore, that only such limitations shall beplaced thereon as are imposed by the prior art or are specifically setforth in the appended claims.

I claim as my invention 1. In a system of modulation, an antenna, anevacuated electrical device comprising a cathode, an anode and acontrolling grid operatively associated with said antenna and adapted toproduce oscillating currents therein, a space-current device having aspace-current path connected in shunt relation to said cathodeand tosaid grid, a source of modulating currents and means i or varying. theelectron emission from one of said electrodes in accordance with saidmodulating currents, said space-current device having a gas containedtherein tending to reduce the temperature variations necessary foreffective modulation.

2. In a system of modulation, an antenna, an evacuated electric devicecomprising a cathode, an anode and a controlling grid 0perativelyassociated with said antenna and adapted to produce oscillating currentstherein, a space-current device having a space-current path connected inshunt relation to said cathode and to said grid, a source of modulatingcurrents and means for varying the electron emission from one of saidelectrodes in accordance with said modulating currents, saidspace-current device including hydrogen gas whereby the temperaturevariations necessary for effective modulation may be decreased.

3. In a radio device, a vacuunrtube generator, a grid condenserassociated therewith, a grid leak for said condenser, said grid leakincluding a pair of electron-emitting electrodes.

4. In a radio device, a vacuum-tube generator, a grid condenserassociated therewith, a grid leak for said condenser, said grid leakincluding a gas-tilled tube and a pair of electron-emitting electrodestherein.

5. In a radio device, a vaccum-tube generator, a grid condenserassociated therewith, a grid leak for said condenser, said grid leakincluding a gas-filled tube, a pair of electron-emitting electrodesthereia, and signal-controlled means for varying the space-currentresistance between said electrodes.

In testimony whereof, I have hereunto subscribed my name thistwenty-sixth day of August, 1921.

QUINCY A. BRACKETT.

